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Evidence of specialized tissue in human interatrial septum: histological, immunohistochemical and ultrastructural findings.

Mitrofanova LB, Gorshkov AN, Lebedev DS, Mikhaylov EN - PLoS ONE (2014)

Bottom Line: The height of the structure on transverse sections positively correlated with age (P = 0.03) and AF history (P = 0.045).Immunohistochemistry showed positive staining of the cells for HCN4 and Caveolin3.Further investigations are warranted to explore electrophysiological characteristics of this structure.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, Federal Almazov Medical Research Centre, Saint-Petersburg, Russia.

ABSTRACT

Background: There is a paucity of information on structural organization of muscular bundles in the interatrial septum (IAS). The aim was to investigate histologic and ultrastructural organization of muscular bundles in human IAS, including fossa ovalis (FO) and flap valve.

Methods: Macroscopic and light microscopy evaluations of IAS were performed from postmortem studies of 40 patients. Twenty three IAS specimens underwent serial transverse sectioning, and 17--longitudinal sectioning. The transverse sections from 10 patients were immunolabeled for HCN4, Caveolin3 and Connexin43. IAS specimens from 6 other patients underwent electron microscopy.

Results: In all IAS specimens sections the FO, its rims and the flap valve had muscle fibers consisting of working cardiac myocytes. Besides the typical cardiomyocytes there were unusual cells: tortuous and horseshoe-shaped intertangled myocytes, small and large rounded myocytes with pale cytoplasm. The cells were aggregated in a definite structure in 38 (95%) cases, which was surrounded by fibro-fatty tissue. The height of the structure on transverse sections positively correlated with age (P = 0.03) and AF history (P = 0.045). Immunohistochemistry showed positive staining of the cells for HCN4 and Caveolin3. Electron microscopy identified cells with characteristics similar to electrical conduction cells.

Conclusions: Specialized conduction cells in human IAS have been identified, specifically in the FO and its flap valve. The cells are aggregated in a structure, which is surrounded by fibrous and fatty tissue. Further investigations are warranted to explore electrophysiological characteristics of this structure.

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An IAS with the flap valve.The heart obtained from a heart of a 62-year-old female patient. A: A transverse section of the IAS. FO, fossa ovalis; FV, flap valve; LA, left atrium; RA, right atrium. Muscle fibers are shown by purple arrowheads. Black asterisks denote localization of the structure. B, C and D: Light micrographs of consecutive sections of the flap valve; (hematoxylin-eosin; ×50). The sections performed along the flap valve form its basis (A) to the middle part (B), and distally at the central part of the FO. B. Atypical myocytes (specialized-like) are in direct contact with contraction myocardium in the upper part of the interatrial septum. C and D. Along the further course of the structure, it is surrounded by fibrous and fatty tissue. *Typical working cardiomyocytes; †atypical specialized-like myocytes; End, endocardium; fibrous tissue is marked by red arrowheads, fatty tissue is marked by green arrowheads.
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pone-0113343-g002: An IAS with the flap valve.The heart obtained from a heart of a 62-year-old female patient. A: A transverse section of the IAS. FO, fossa ovalis; FV, flap valve; LA, left atrium; RA, right atrium. Muscle fibers are shown by purple arrowheads. Black asterisks denote localization of the structure. B, C and D: Light micrographs of consecutive sections of the flap valve; (hematoxylin-eosin; ×50). The sections performed along the flap valve form its basis (A) to the middle part (B), and distally at the central part of the FO. B. Atypical myocytes (specialized-like) are in direct contact with contraction myocardium in the upper part of the interatrial septum. C and D. Along the further course of the structure, it is surrounded by fibrous and fatty tissue. *Typical working cardiomyocytes; †atypical specialized-like myocytes; End, endocardium; fibrous tissue is marked by red arrowheads, fatty tissue is marked by green arrowheads.

Mentions: In all 23 (100%) specimens the FO, its rims and the flap valve had muscle fibers consisting of contraction cardiac myocytes (Figure 2a, b). Immediately below the endocardium among typical contraction myocytes in the muscular bundles, in the flap valve, antero-superior FO rim, and in the FO, there were tortuous and horseshoe-shaped intertangled myocytes that formed fan-shaped, X-shaped, Y-shaped, and other figures. These cells were found in all 23 (100%) cases, and they were aggregated into a definite structure in 21 (91%) cases (Table 1). The structure was extended from the flap valve to the FO, and to its antero-superior rim. The tortuous myocytes had a mean diameter of 12.4±4.3 (8.4–16.0) µm, and a length of 40–250 µm (Figure 3). In the centre of this structure myocytes were shorter, and on the periphery they were longer. Besides this type of cells, there were small (8.1±3.3 (5.2–10.0) µm) rounded myocytes with pale cytoplasm, and large (28.5±11.7 (25.5–40.0) µm) rounded myocytes with pale cytoplasm. According to their histological characteristics the myocytes were similar to specialized conduction cells: (1) the tortuous myocytes - like T-cells; (2) the small rounded cells with pale cytoplasm - like pacemaker P-cells of the sinoatrial and AV nodes; (3) the large pale myocytes – like Purkinje cells (Figure 3).


Evidence of specialized tissue in human interatrial septum: histological, immunohistochemical and ultrastructural findings.

Mitrofanova LB, Gorshkov AN, Lebedev DS, Mikhaylov EN - PLoS ONE (2014)

An IAS with the flap valve.The heart obtained from a heart of a 62-year-old female patient. A: A transverse section of the IAS. FO, fossa ovalis; FV, flap valve; LA, left atrium; RA, right atrium. Muscle fibers are shown by purple arrowheads. Black asterisks denote localization of the structure. B, C and D: Light micrographs of consecutive sections of the flap valve; (hematoxylin-eosin; ×50). The sections performed along the flap valve form its basis (A) to the middle part (B), and distally at the central part of the FO. B. Atypical myocytes (specialized-like) are in direct contact with contraction myocardium in the upper part of the interatrial septum. C and D. Along the further course of the structure, it is surrounded by fibrous and fatty tissue. *Typical working cardiomyocytes; †atypical specialized-like myocytes; End, endocardium; fibrous tissue is marked by red arrowheads, fatty tissue is marked by green arrowheads.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4239074&req=5

pone-0113343-g002: An IAS with the flap valve.The heart obtained from a heart of a 62-year-old female patient. A: A transverse section of the IAS. FO, fossa ovalis; FV, flap valve; LA, left atrium; RA, right atrium. Muscle fibers are shown by purple arrowheads. Black asterisks denote localization of the structure. B, C and D: Light micrographs of consecutive sections of the flap valve; (hematoxylin-eosin; ×50). The sections performed along the flap valve form its basis (A) to the middle part (B), and distally at the central part of the FO. B. Atypical myocytes (specialized-like) are in direct contact with contraction myocardium in the upper part of the interatrial septum. C and D. Along the further course of the structure, it is surrounded by fibrous and fatty tissue. *Typical working cardiomyocytes; †atypical specialized-like myocytes; End, endocardium; fibrous tissue is marked by red arrowheads, fatty tissue is marked by green arrowheads.
Mentions: In all 23 (100%) specimens the FO, its rims and the flap valve had muscle fibers consisting of contraction cardiac myocytes (Figure 2a, b). Immediately below the endocardium among typical contraction myocytes in the muscular bundles, in the flap valve, antero-superior FO rim, and in the FO, there were tortuous and horseshoe-shaped intertangled myocytes that formed fan-shaped, X-shaped, Y-shaped, and other figures. These cells were found in all 23 (100%) cases, and they were aggregated into a definite structure in 21 (91%) cases (Table 1). The structure was extended from the flap valve to the FO, and to its antero-superior rim. The tortuous myocytes had a mean diameter of 12.4±4.3 (8.4–16.0) µm, and a length of 40–250 µm (Figure 3). In the centre of this structure myocytes were shorter, and on the periphery they were longer. Besides this type of cells, there were small (8.1±3.3 (5.2–10.0) µm) rounded myocytes with pale cytoplasm, and large (28.5±11.7 (25.5–40.0) µm) rounded myocytes with pale cytoplasm. According to their histological characteristics the myocytes were similar to specialized conduction cells: (1) the tortuous myocytes - like T-cells; (2) the small rounded cells with pale cytoplasm - like pacemaker P-cells of the sinoatrial and AV nodes; (3) the large pale myocytes – like Purkinje cells (Figure 3).

Bottom Line: The height of the structure on transverse sections positively correlated with age (P = 0.03) and AF history (P = 0.045).Immunohistochemistry showed positive staining of the cells for HCN4 and Caveolin3.Further investigations are warranted to explore electrophysiological characteristics of this structure.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, Federal Almazov Medical Research Centre, Saint-Petersburg, Russia.

ABSTRACT

Background: There is a paucity of information on structural organization of muscular bundles in the interatrial septum (IAS). The aim was to investigate histologic and ultrastructural organization of muscular bundles in human IAS, including fossa ovalis (FO) and flap valve.

Methods: Macroscopic and light microscopy evaluations of IAS were performed from postmortem studies of 40 patients. Twenty three IAS specimens underwent serial transverse sectioning, and 17--longitudinal sectioning. The transverse sections from 10 patients were immunolabeled for HCN4, Caveolin3 and Connexin43. IAS specimens from 6 other patients underwent electron microscopy.

Results: In all IAS specimens sections the FO, its rims and the flap valve had muscle fibers consisting of working cardiac myocytes. Besides the typical cardiomyocytes there were unusual cells: tortuous and horseshoe-shaped intertangled myocytes, small and large rounded myocytes with pale cytoplasm. The cells were aggregated in a definite structure in 38 (95%) cases, which was surrounded by fibro-fatty tissue. The height of the structure on transverse sections positively correlated with age (P = 0.03) and AF history (P = 0.045). Immunohistochemistry showed positive staining of the cells for HCN4 and Caveolin3. Electron microscopy identified cells with characteristics similar to electrical conduction cells.

Conclusions: Specialized conduction cells in human IAS have been identified, specifically in the FO and its flap valve. The cells are aggregated in a structure, which is surrounded by fibrous and fatty tissue. Further investigations are warranted to explore electrophysiological characteristics of this structure.

Show MeSH
Related in: MedlinePlus